Photonic Crystal Waveguide Research Articles

Photonic crystal terahertz wave logic AND-XOR gate

Terahertz wave logic gates are one of the key devices required in terahertz wave communication systems and signal processing systems. In this paper, we design a logic gate to realize the function of AND gate and XOR gate. The logic AND-XOR gate is based on two large photonic crystal ring resonators, one small ring resonator and photonic crystal branch waveguides. The structure is analyzed and simulated by treating the plane wave expansion and finite difference time domain methods. The steady-state field distributions and output power characteristics of the gate are analyzed. The simulation results show that the designed device with the feasibility can be used in terahertz wave integrated digital circuit.

Prism lens for beam collimation in a silicon photonic crystal beam-steering device.

The doubly periodic Si photonic crystal waveguide operates as a nonmechanical beam-steering device that can be applied in light detection and ranging. In this Letter, we develop and describe a prism lens that collimates a fan-shaped beam, emitted from the waveguide independent of the steering angle. Its fundamental profile is investigated using a theoretical analysis for thick lenses, and then, its detailed aspherical design is obtained. In ray tracing, this prism lens suppresses the beam divergence to less than the diffraction limit in most of the targeted beam-steering range. The prism lens is fabricated by acrylic cutting, and its expected characteristics are observed.

Coupling of a whispering gallery mode to a silicon chip with photonic crystal.

We demonstrate the efficient coupling (99.5%) of a silica whispering gallery mode microresonator directly with a silicon chip by using a silicon photonic crystal waveguide as a coupler. The efficient coupling is attributed to the small effective refractive index difference between the two devices. The large group index of the photonic crystal waveguide mode also contributes to the efficient coupling. A coupling Q of 2.68×106 is obtained, which allows us to achieve the critical coupling of a silica whispering gallery mode with an intrinsic Q of close to 107 with a Si chip.

Double-layer graphene on photonic crystal waveguide electro-absorption modulator with 12 GHz bandwidth

Abstract Graphene has been widely used in silicon-based optical modulators for its ultra-broadband light absorption and ultrafast optoelectronic response. By incorporating graphene and slow-light silicon photonic crystal waveguide (PhCW), here we propose and experimentally demonstrate a unique double-layer graphene electro-absorption modulator in telecommunication applications. The modulator exhibits a modulation depth of 0.5 dB/μm with a bandwidth of 13.6 GHz, while graphene coverage length is only 1.2 μm in simulations. We also fabricated the graphene modulator on silicon platform, and the device achieved a modulation bandwidth at 12 GHz. The proposed graphene-PhCW modulator may have potentials in the applications of on-chip interconnections.

Dispersion Engineering With Photonic Inverse Design

Dispersion engineering, such as the design of slow light waveguide systems, is an effective tool for a wide range of photonic applications, but presents a difficult optical design challenge. Most applications require a slow light waveguide design that mitigates group velocity dispersion, and efficient coupling solutions over the slow light operating bandwidth. In this work, we optimize the slow light dispersion relation of a photonic crystal waveguide with three dimensional (3D) inverse design methods. In addition, we design mode couplers for the photonic crystal waveguide. The optimized waveguide supports a slow light mode with a group index of n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 25 and a normalized bandwidth group index product of of 0.38. A compact mode coupler to a strip waveguide is designed with an average efficiency of 92.7% within the slow light operating bandwidth. Lastly, we design a fully etched grating which couples directly to the slow light mode with a 32.5% average efficiency.

Chiral cavity quantum electrodynamics with coupled nanophotonic structures

Up to now it remains challenging to couple photons from a circularly polarized emitter into a photonic structure to simultaneously realize strong photon-emitter interaction and unidirectional propagation locked by local helicity of the optical mode at the nanoscale. In this paper we propose a unique approach that combines a photonic crystal and metallic nanoparticle structure to create nanocavities with both strong local-field intensity and high helicity. In this system the rate of circularly polarized photons emitting into the photonic crystal waveguide reaches $148{\ensuremath{\gamma}}_{0}$, which is one order of magnitude larger than that without the nanoparticle, and in the ultranarrow band-edge mode the linewidth of Rabi splitting spectra is about one-tenth of that with the nanoparticle only, both with $\ensuremath{\approx}95%$ of photons propagating unidirectionally along the nanoscale waveguide. We suggest that our paper establishes a nanophotonic interface of chiral quantum electrodynamics for on-chip nonreciprocal quantum light sources, quantum circuits, and scalable quantum networks.

Embedded waveguide band: New localized states from parity-time symmetric photonic crystal waveguide

Using conventional photonic crystal waveguides combined with the Parity-Time (PT) symmetry configuration, we study the evolution of the waveguide mode bands, and the mechanism of the band merging and the exceptional point forming. A special waveguide mode band occurs in the band evolution with a part of the band embedded in the bulky bands. The embedded band takes on a new localized state with its mode field is mainly localized in the waveguide. The frequency on the bottom of the embedded band excites a huge localized field. The exceptional point on the special band excites an asymmetric mode field in the waveguide and an amplified transmission.

Photonic crystal waveguide for difference frequency generation in terahertz range

We consider a waveguided semiconductor structure with photonic crystal core for efficient difference frequency generation. The calculation of the dispersion of the eigenmodes shows that this structure pumped by radiation with wavelengths of 1000 and 1003 nm, allows the difference frequency generation at 1 THz with a coherence length of 1 cm.

Magneto-Optical Isolator Based on Ultra-Wideband Photonic Crystals Waveguide for 5G Communication System

This paper presents a novel magneto-optical isolator based on an ultra-wideband and high efficiency photonic crystals (PCs) waveguide and gyromagnetic ferrites. The three-dimensional numerical simulation finds that the photonic crystals waveguide’s (PCW) transmission efficiency rises with its height and width. The corresponding experiments are performed by using a triangular lattice Al2O3 dielectric posts array in 5G millimeter wave band. The measured transmission efficiency is up to 90.78% for the optimal PCs waveguide structure, which has ultra-wide operating bandwidth from 23.45 to 31.25 GHz. The magneto-optical isolator is designed by inserting two rectangular gyromagnetic ferrites into the PCs waveguide. Due to the contrast between the effective permeability of the left and right circular polarization waves passing through the magnetized ferrite sheets, the ferromagnetic resonance absorption of the forward and reverse waves is different. By using finite element method, the isolation is optimized to be 49.49 dB for the isolator and its relative bandwidth reaches 8.85%. The high isolation, broadband, and easy integration indicate that our designed magneto-optical isolator has significant advantage in 5G communication systems.

Design and analysis of a 09 Tb/s six-channel WDM filter based on photonic crystal waveguides

A six-channel wavelength-division multiplexing filter is proposed in this paper, based on a two-dimensional rods-in-air square-lattice photonic crystal (PhC) slab structure. The plane wave expansion method is applied to compute the band structure of the PhC. Three-dimensional finite-difference time-domain simulation methodology is used to measure and analyze the performance of the filter. Performances for both the 2D and 3D designs of the structure are analyzed. The analyses show that the device is capable of filtering six different wavelengths, i.e., 1310 nm, 1415 nm, 1455 nm, 1550 nm, 1725 nm, and 1770 nm. Owing to its linear optical operation, the device is able to operate at low power and also offers a high data rate in the range of $ \approx 0.9\,\,{\rm Tb/s} $≈0.9Tb/s to $ \approx 4\,\,{\rm Tb/s} $≈4Tb/s. Moreover, the footprint area of the proposed device is on the order of $ {165}\,\,{{\unicode{x00B5}{\rm m}}^2} $165µm2, which is suitable for high-density integration of photonic circuits.

Augmenting performance of a MEMS cantilever-based photonic crystal waveguide for switching applications.

In this paper, a micro-electro-mechanical system-based cantilever is integrated as a line defect on a photonic crystal silicon slab for optical switching applications. The elliptical holes are etched in the photonic crystal waveguide that result in wide transmission bandwidth of 56 nm in comparison to etched circular holes in the structure with a footprint of only ${12.5}\,\,{\unicode{x00B5}{\rm m}} \times {8}\,\,{\unicode{x00B5}{\rm m}}$12.5µm×8µm. The device is optimized for variation in height, the lattice constant, and semi-major and semi-minor axes in the optical range of the S-C-L band. It is shown that the response rise time of the device is 21 µs with very high extinction ratio of 30.4 dB and low insertion loss of 0.32 dB.

Design of One-Bit Magnitude Comparator using Photonic Crystals

Abstract At present, photonic crystals (PhCs) are used to design various combinational and sequential circuits. In this paper, an all-optical one-bit magnitude comparator is proposed using PhC waveguide without using nonlinear material. It is based on beam interference principle, using T-shaped lattice with silicon dielectric rods in air background. It is demonstrated through finite-difference time-domain simulation and verified numerically using MATLAB simulation. The size of PhC lattice structure can be as small as 19.167a×19.167a, where ‘a’ is the lattice constant of the PhC.

Wideband Slow Light in a Line-defect Annular Photonic-crystal Waveguide

In this theoretical study, a line-defect photonic-crystal waveguide hosted in an annular photonic crystal was demonstrated to provide high-performance slow light with a wide band, low group-velocity dispersion, and a large normalized delay-bandwidth product. Combined with structural-parameter optimization and selective optofluid injection, the normalized delay-bandwidth product could be enhanced to a large value of 0.502 with a wide bandwidth of 58.4 nm in the optical-communication window, for a silicon-on-insulator structure. In addition, the group-velocity dispersion is on the order of 105 (ps2/km) in the slow-light region, which could be neglected while keeping the signal transmission unchanged.

Numerical optimization design for waveguide bends with low-loss and wide-bandwidth in two-dimensional photonic crystal slabs

In this paper, we demonstrate some optimization designs for waveguide bends in two-dimensional photonic crystal slabs based on the effective index approximation. Four different types of waveguide bends with low-loss and wide-bandwidth are designed, which involve 60°, Z-shaped, Y-shaped and 120° waveguide bends in the two-dimensional triangular lattice photonic crystals. In all numerical experiments, the electromagnetic fields in the photonic crystal slab waveguides are solved by the finite element method in COMSOL software. Several strategies are applied to design slab waveguide bends with low-loss and wide-bandwidth, for example, adding some elliptical air-holes near the corner or adjusting the radii of some air-holes. For four optimized structures, the transmission efficiencies at 1550 nm are all more than 92%. As we show, this is achieved over a −0.915 dB bandwidth of more than 65 nm in all waveguide bends. The numerical results indicate that the design scheme we applied to optimize waveguide bends in photonic crystal slabs is simple and efficient, which can provide some useful guidance for further three-dimensional design.

Enhancement of magneto-optical properties in magnetic photonic crystal slab waveguide based on yttrium iron garnet

In this work, a polarization-independent waveguide based on magnetic photonic crystal (MPC) with a triangular lattice of air holes in Yttrium Iron Garnet (YIG) slab grown on alumina (Al2O3) substrate is proposed, where both TE-like and TM-like periodic band gaps overlap. YIG is well known for its attracting magneto-optical (MO) properties and used to produce a coupling between the TE and TM modes. Thus, a nonreciprocal effect can be obtained by applying an external magnetic field parallel to the direction of propagation. At 1550 nm, the complete photonic band gap is simulated and optimized using the three dimensional plane-wave expansion method. The aim of this study is to enhance Faraday rotation (FR) while maintaining a low modal birefringence. A numerical analysis in function of magnetic gyration (g) has been reported, using the BeamProp software. The results reveal a proportional relation between FR, Δn and g, such for g = 0.5, a large FR of 26.11×104 °/cm with Δn = 7×10−6. The results show a real improvement of this MPC structure based on YIG with larger FR, lower modal birefringence and minimal losses. The notable enhancement in the MO behaviour could improve the performance of optical isolators, and makes it suitable for nonreciprocal devices.

Theory of soliton propagation in nonlinear photonic crystal waveguides.

Propagation of the temporal soliton in Kerr-type photonic crystal waveguide is investigated theoretically and numerically. An expression describing the evolution of the envelope of the soliton based on the full-wave modal analysis, taking into account all space-harmonics, is rigorously obtained. The nonlinear coefficient is derived, for the first time, based on a modification of the refractive indices for each space-harmonic due to the Kerr-type nonlinearity. For illustrating the general formulation and results, we performed extensive computational electromagnetics simulations for the propagation of gap solitons in an experimentally feasible photonic crystal waveguides, endorsing the correctness and usefulness of the proposed formalism.

Exploiting Long-Range Disorder in Slow-Light Photonic Crystal Waveguides: Anderson Localization and Ultrahigh Q/V Cavities

The interplay between order and disorder in photonic lattices opens up a wide range of novel optical scattering mechanisms, cavity-mode resonances, and applications that can be obscured by typical ordered design approaches to photonics. Striking examples include Anderson localization, random lasers, and visible light scattering in biophotonic structures such as butterfly wings. In this work, we present a profound example of light localization in photonic crystal waveguides by introducing long-range correlated disorder. Using a rigorous three-dimensional Bloch mode expansion technique, we demonstrate how interhole correlations have a negative contribution to the total out-of-plane radiative losses, leading to a pronounced enhancement of the quality factor, Q, and Q/V cavity figures of merit in the long-range correlation regime. Subsequently, the intensity fluctuations of the system are shown to globally increase with the correlation length, highlighting the nontrivial role of long-range disorder on the underlying scattering mechanisms. We also explore the possibility of creating ultrahigh quality cavity modes via interhole correlations, which have various functionalities in chip-based nonlinear optics and waveguide cavity-quantum electrodynamics.

TE band structure in a photonic waveguide with triangular holes

This study determines the TE band structures in a two-dimensional photonic crystal waveguide with triangular dispersers in a hexagonal lattice in a GaAs background. Using the plane-wave expansion method and the supercell technique, a defective mode propagating in the direction of the linear defect was numerically identified within the photonic band gap. In addition, this study reports that this defective mode may be tuned to higher frequencies by increasing the applied hydrostatic pressure. However, when the triangular dispersers are rotated, no noticeable change is observed in the defective mode within the photonic band gap.

Sensitivity analysis of ring-shaped slotted photonic crystal waveguides for mid-infrared refractive index sensing

In this paper, the sensitivity of slotted photonic crystal waveguides (SPCW) with triangular lattice pattern of ring-shaped holes is analyzed in order to realize highly refractive index (RI) sensor devices at mid-infrared wavelengths. The sensing principle is based on the shift of the transmission spectrum edge of these specific ring hole SPCW waveguides giving rise to reinforced light–matter interaction. The 3D simulation results applied to silicon waveguides on membrane show that this guide geometry leads to a very high sensitivity to variations in the ambient environment index, with very dependent trends on the opto-geometric factors of the waveguides. As a matter of example, a $$720 \,\mathrm{nm}$$ wavelength position band edge shift is predicted, corresponding to a sensitivity of more than $$1450 \,\mathrm{nm}$$ per refractive index unit with a device insertion loss level of $$-\,3 \,\mathrm{dB}$$ .

Efficient mode converter to deep-subwavelength region with photonic-crystal waveguide platform for terahertz applications.

Metallic deep-subwavelength features can aid in integration of microscopic components or strong light-matter interaction with a low-loss dielectric waveguide platform. A mode converter or coupler is required to integrate the devices. However, there is a vast difference in the physical scale and modal distribution between the deep-subwavelength structures and the dielectric waveguide platform. Here, we employ a tapered-slot mode converter to facilitate the electromagnetic wave transition from a gap width smaller than 1/100 of a wavelength (λ) to a larger-scale mode that is amenable to a terahertz (THz) silicon photonic-crystal waveguide. The mode converter is metallic, and fabricated on top of indium phosphide substrate, leading to incongruity with the modal field distribution of the silicon photonic-crystal waveguide. To mitigate this, a sandwiched structure is developed to match the symmetry of the mode of photonic-crystal waveguide, thereby facilitating efficient transfer of energy. For a proof of concept, we integrate a resonant tunneling diode (< 2 µm) as a THz detector in a photonic-crystal waveguide platform in the 0.3-THz band (λ ∼ 1 mm). The coupling efficiency is close to unity (∼90%) with broadband operation (∼50 GHz) in experiments. Thereafter, we employ the developed integrated device as a receiver in a THz communication experiment. In this manner, we successfully achieve real-time error-free data transmission at 32 Gbit/s, and demonstrate wireless transmission of uncompressed 4K high-definition video.